TPO launched a 4G service last month and started migrating its existing 2G and 3G customers onto new deals.

The MVNO also started using Three’s network for its mobile services. It previously used EE.

But some customers encountered long delays between activating their new SIM and their old phone number being ported across, leaving them unable to be contacted.

Customers also complained about TPO’s handling of the situation, saying that calls to its customer services department were not answered and that the provider’s online chat option was “nearly always off”.

Mr Epstein said: “Since launching 4G, there has been a significant demand from customers wanting to switch over and we have experienced an unusually high number of customer contacts.

“As a result, some customers have had to wait longer than usual to get through to an agent on the phone, we have alternative online contact options which are regularly repeated while waiting on the line.

“For 240 people their number transfer took significantly longer than usual, we endeavoured to keep these customers informed through regular communications.

“While customers had use of a temporary number, we understand the significant inconvenience caused by the delay and our team did all they can to resolve the delay as quickly as possible and we’re very sorry for disruption to their service.

“The issue has now been resolved for almost all that were affected.”

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